If you are undertaking this as a serious business venture as opposed to creating a video site as a hobby you certainly have your work cut out for you.
Firstly regardless of the size of social video sites they are all based on the same cash flow model - which is 99.9% advertising generated.
This means that no matter how good your script is, you need traffic and that equates to 'Market Share' in a general business sense.
YouTube, LiveLeak, RedTube, XTube, break.com, metacafe.com are just some of your competitors on the business level and all are ranked in the top few hundred websites in the world commanding a huge satisfied market share.
So in terms of 'how profitable' you need to carry out your research regarding your niche market and find out the Maximum potential traffic your target market could attract on a monthly basis.
At the start the majority of your income will be CPC or CPM (unless you have a sales team to sell fixed price ads or co-brand with major companies). If your income is only CPC or CPM work out your estimated CTR rate and traffic rates and you can the forecast your revenue.
Obviously though like most video sites if you take off, ensure you have cashflow to cover your bandwidth costs and server costs. Users are lazy and impatient so if you wish to compete with other companies (there must be some competitors to your market) you need to be faster, attractive and most of all Free to use.
Also try and make your site accessible to everyone and not only to people who sign up.
In regards to scripts i dont personally know any out there that really compete with the major video sites at all. I have dabbled with a few which are all preety bad IMHO and blatently just copy the current video sites (which means you offer no added benefit whilst having no current market or user activity).
You would be best off using individual scripts for the tehcnical part of uploading, converting and thumbnailing videos, whilst writing or a hire custom designers and programmers to merge them together in a Unique way that offers the user something new.
If you use ASP.net i can provide you with scripts via PM to Upload Multiple Videos, Convert the videos to Flash Video Files automatically, rename them securily, create various thumbnails of the video with watermarks, capture the videos information such as length and finally add the video to the database.
The videos can than be played via any 'Flash video player' there are many scripts out there just search on google. Though you will need to purchase the actual FLASH File and not just the SWF file, this way you can change the video players appearance and make it your own.
Hope that all helps
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